Light weight parallel manipulators using active/passive cables

ABSTRACT

The present invention provides parallel, cable based robotic manipulators, for use in different applications such as ultra high-speed robots or positioning devices with between three to six degrees of freedom. The manipulators provide more options for the number of degrees of freedom and also more simplicity compared to the current cable-based robots. The general structure of these manipulators includes a base platform, a moving platform or end effector, an extensible or telescoping central post connecting the base to moving platform to apply a pushing force to the platforms. The central post can apply the force by an actuator (active), or spring or air pressure (passive) using telescoping cylinders. The robotic manipulators use a combination of active and passive tensile (cable) members, and collapsible and rigid links to maximize the benefits of both pure cable and conventional parallel mechanisms. Different embodiments of the robotic manipulators use either active cables only, passive cables only, or combinations of active and passive cables. An active cable is one whose length is varied by means of a winch. A passive cable is one whose length is constant and which is used to provide a mechanical constraint. These mechanisms reduce the moving inertia significantly to enhance the operational speed of the robots. They also provide a simpler, more cost effective way to manufacture parallel mechanisms for use in robotic applications.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This patent application relates to, and claims the prioritybenefit from, U.S. Provisional Patent Application Serial No. 60/394,272filed on Jul. 9, 2002 and which is incorporated herein in its entirety.

FIELD OF THE INVENTION

[0002] This invention relates to robotic manipulators for moving andpositioning an object in space, and more particularly the presentinvention relates to light weight cable actuated active/passive parallelmanipulators.

BACKGROUND OF THE INVENTION

[0003] Robotic manipulators may be divided into two main categories,parallel and serial manipulators. Serial manipulators, which are morecommon in the industry, have several links in series usually connectedby rotary or sliding joints. They are analogous to the human arm whichhas a series of links hinged at the shoulder, elbow and wrist. Theconfiguration of serial manipulators necessitates the location of thedriving motors to be at the joints themselves or the use of a heavy orcomplicated linkage for transferring the motion from the base of therobot to the joints. This is a disadvantage since it requires themovement of the large mass of the manipulator and drives even for asmall payload. Further, the positional error of the end effector of aserial manipulator is the accumulation of the errors in the individuallinks so that by increasing the size or number of links the errorassociated with the position of the end effector increases.

[0004] In contrast to serial manipulators, the links of a parallelmanipulator function in parallel to determine the movement of the endeffector. A flight simulator and camera tripod are two examples of thiskind of mechanisms. If one of the legs of a tripod is extended or moved,it changes the position of the end point. Parallel manipulators haverelatively lower mass to payload ratio since the links work together andthe actuators are mounted on a stationary base. They also have betterprecision since the error in the end effector is in the same order ofactuators' error.

[0005] Low inertia, and therefore, high speed manipulation is one of themain applications of parallel robots. U.S. Pat. No. 4,976,5821 issued toClavel, entitled ‘Device for the Movement of and Positioning of anElement in Space’, and reported further in Clavel, ‘Delta, a Fast Robotwith Parallel Geometry’, Proceeding of International Symposium onIndustrial Robots, pp. 91-100, April 1988, discloses one of the mostsuccessful mechanisms of this kind which produces movement with threepure translational degrees of freedom at its end effector. In thismanipulator of Clavel, rotating arms are connected to the end effectorusing three parallelograms. The parallelograms constrain the endeffector to be parallel to the base plate at all times and therefore,three pure translational movements are achieved.

[0006] Other manipulator designs such as disclosed in L-W. Tsai,‘Kinematic of a Three-DOF Platform With Extensible Limbs’, Proceeding ofthe Conference of Recent Advances in Robot Kinematics, pp. 401-410,1996,also provide pure translational movement of the end effector with threetranslational degrees of freedom. In the Tsai mechanism, three linearactuators connect the end effector to the stationary platform withuniversal joints. The specific configuration of the universal jointsguarantees the three translational motions of the end effector.

[0007] There are also parallel mechanism robots with 6-DOF such as thehexa pod, see Griffis M., Crane C., et Duffy J., ‘A smart kinestaticinteractive platform’, In ARK, pp. 459-464, Ljubljana, 4-6 July 1994,and the hexa robot disclosed in U.S. Pat. No. 5,333,514 issued to Toyamaet al. entitled ‘Parallel Robot’.

[0008] In general, parallel mechanism robots have higher stiffness toweight ratio, moment and torque capacity, and better accuracy. They alsobenefit from a simpler mechanism due to the elimination of drive trainsand, also lower moving mass due to the stationary location of theactuators. Further reduction in the moving inertia of parallelmechanisms may be achieved by replacing the rigid links with tensilemeans such as cables. Replacing the rigid arms not only reduces themoving inertia but it lowers manufacturing cost and simplifies themechanism structure by eliminating many joints.

[0009] Using cables in cranes such as disclosed in U.S. Pat. No.3,286,851 issued to J. R. Sperg entitled ‘Cargo Handling Rig’, andsimilar applications, see U.S. Pat. No. 5,967,72910 issued to G. F. Foesentitled ‘Bottom Discharge Rotating Ring Drive Silo Unloader’, is olderthan robotics, however in recent years several attempts have been madeto design cable actuated manipulators. Some of these manipulators aredesigned to imitate human arms and can be considered as serialmanipulators with parallel actuators, see U.S. Pat. No. 3,631,737 issuedto F. E. Wells entitled ‘Remote Control Manipulator for Zero GravityEnvironment’; U.S. Pat. No. 3,497,083 issued to V. C. Anderson, R. C.Horn entitled ‘Tensor Arm Manipulator’; and U.S. Pat. No. 4,683,773issued to G. Diamond entitled ‘Robotic Device’.

[0010] A pure parallel cable actuated mechanism is disclosed in S.Kawamura, W. Choe, S. Tanaka, S. R. Pandian, ‘Development of anultrahigh Speed Robot FALCON using Wire Drive System’, Proceeding ofIEEE Conference on Robotics and Automation, pp. 215-220, 1995. Thismanipulator has seven active cables to provide 6-DOF for the endeffector. This mechanism does not have any rigid link in its structureand the cables are extended in both sides to maintain tension in thecables.

[0011] U.S. Pat. No. 4,666,362 issued to S. E. Landsberger and T. B.Sheridan entitled ‘Parallel Link Manipulator’ discloses a manipulatorwhich uses six active cables and a passive collapsible link. Thecollapsible link applies a pushing force between the moving andstationary platforms in order to keep all cables in tension.

[0012] U.S. Pat. No. 5,313,854 issued to H. A. Akeel entitled ‘LightWeight Robot Mechanism’, discloses another combined cable-collapsiblemechanism which moves the end point of the collapsible shaft in thespace but does not have any control on its orientation.

SUMMARY OF THE INVENTION

[0013] Based on the advantages of parallel and cable based manipulators,some new designs are introduced in this work which can be used in ultrahigh-speed robots with 3 to 6 degrees of freedom. The robotic mechanismsdisclosed herein provide more options for the number of degrees offreedom and also more simplicity compared to the current cable-basedrobots. In the proposed designs a combination of active and passivetensile members, collapsible and rigid links are used to maximize thebenefits of both pure cable and parallel mechanisms.

[0014] Applications of both passive and active cables in the new designsimprove performance, simplicity and feasibility of the robots. An activecable is one whose length is varied by means of a rotating drum. Apassive cable is one whose length is constant and which is used toprovide a mechanical constraint. In general, compared to rigid linkparallel mechanisms the robotic mechanisms disclosed hereinadvantageously reduce the moving inertia significantly to enhance theoperational speed of the robots. They also provide a simpler, more costeffective way to manufacture parallel mechanisms for use in roboticapplications, measurements, and entertainments.

[0015] The design of new light weight parallel manipulators forhigh-speed robots using active/passive cables is explained herebelow.The general structure of these manipulators has the following maincomponents (see FIGS. 1 and 2):

[0016] a) A base platform 24.

[0017] b) A moving platform or end effector 22.

[0018] c) An extensible or telescoping central post 26 connecting thebase 24 to moving platform 22 to apply a pushing force to the platforms.The central post can apply the force by an actuator (active) or springor air pressure (passive); and

[0019] d) Active cables 28. Active cables are those whose lengths changeusing an actuator; and/or

[0020] e) Passive cables 42. Passive cables are cables whose lengths arefixed.

[0021] The robotic mechanism may have just active cables, just passivecables, or a combination of both.

[0022] In one aspect of the invention there is provided a roboticmechanism, comprising:

[0023] a support base, an end effector and a biasing member havingopposed ends and attached at one of said opposed ends to the supportbase and attached at the other of said opposed ends to the end effector;and

[0024] at least three cables each connected at a first end thereof tosaid end effector and said at least three cables having second endsbeing attached to an associated positioning mechanism for retracting ordeploying each of said at least three cables to position said endeffector in a selected position in space, said biasing member applyingforce on the end effector with respect to the support base formaintaining tension in said at least three cables.

[0025] The present invention also provides a robotic mechanism,comprising:

[0026] a support base, an end effector and a biasing member havingopposed ends and pivotally attached at one of said opposed ends to thesupport base and pivotally attached at the other of said opposed ends tothe end effector; and

[0027] six cables each connected at a first end thereof to said endeffector and said six cables having second ends being attached to anassociated positioning mechanism for moving the second ends of theassociated cable independently of the other cables, said biasing memberapplying force on the end effector with respect to the support base formaintaining tension in said six cables, wherein movement of the secondends of the cables by the associated positioning mechanisms changes aposition and orientation of the end effector so that the roboticmechanism has six degrees of freedom.

[0028] The present invention also provides a five-degree-of-freedomrobotic mechanism, comprising:

[0029] a support base, an end-effector and a biasing member havingopposed ends and pivotally attached at one of said opposed ends to thesupport base with a universal joint and pivotally attached at the otherof said opposed ends to the end-effector with a universal joint; and

[0030] five cables each connected at a first end thereof to said endeffector and said five cables having second ends being attached to anassociated positioning mechanism for moving the second ends of theassociated cable independently of the other cables, said biasing memberapplying force on the end effector with respect to the support base formaintaining tension in said five cables, wherein movement of the secondends of the cables by the associated positioning mechanisms changes aposition and orientation of the end-effector.

[0031] The present invention also provides a robotic mechanism,comprising:

[0032] an end effector, a post having opposed ends being pivotallyconnected at one of said opposed ends to the end effector;

[0033] a support base defining a plane and having a hole extendingtherethrough, an outer ring structure pivotally connected to saidsupport base within said hole for pivotal motion of said outer ringstructure out of the plane of said support base, a first actuator forpivoting said outer ring structure, an inner ring structure pivotallymounted to said outer ring structure inside said outer ring structure,said inner ring structure being concentric with said outer ringstructure, a second actuator for pivoting said inner ring structure,said inner ring structure having an axis of rotation in the plane of theouter ring, and perpendicular to the axis of rotation of said outer ringstructure, said inner ring structure having a central web with a holetherethrough and a universal joint mounted in said hole to the centralweb, the other end of said post being slidably mounted in said universaljoint, bias means connected to said post for biasing said end effectoraway from said support base;

[0034] a first set of three cables each connected at one end thereof tosaid end effector and the other ends of said first set of three cablesbeing attached to positioning means mounted on said support base forpulling said three cables independently of each other to position saidend effector in a selected position in space; and

[0035] a second set of three cables each connected at one end thereof tosaid end effector and the other ends thereof being attached to the otherend of said post, said second set of three cables being mounted to saidinner ring at substantially 120° with respect to each other andconstrained to be parallel to each other between said end effector andsaid inner ring and wherein when said positioning means moves said endeffector to a selected position in its workspace, said second set ofthree cables maintains said end effector in a plane parallel to theplane of said inner ring.

[0036] The present invention also provides a robotic mechanism,comprising:

[0037] an end effector, a post having opposed ends being pivotallyconnected at one of said opposed ends to the end effector using auniversal joint, the post having an adjustable length;

[0038] a support base defining a plane and having a hole extendingtherethrough, an outer ring structure pivotally connected to saidsupport base within said hole for pivotal motion of said outer ringstructure out of the plane of said support base, a first actuator forpivoting said outer ring structure, an inner ring structure pivotallymounted to said outer ring structure inside said outer ring structure,said inner ring structure being concentric with said outer ringstructure, a second actuator for pivoting said inner ring structure,said inner ring structure having an axis of rotation in the plane of theouter ring, and perpendicular to the axis of rotation of said outer ringstructure, said inner ring structure having a central web with a holetherethrough and a universal joint mounted in said hole to the centralweb, the other end of said post being slidably mounted in said universaljoint,;

[0039] a first set of three cables each connected at one end thereof tosaid end effector and the other ends of said first set of three cablesbeing attached to a positioning mechanism mounted on said support basefor pulling said three cables independently of each other to positionsaid end effector in a selected position in space; and

[0040] a second set of three cables each connected at one end thereof tosaid end effector and the other ends thereof being attached to, a winchmounted on said central web of the inner ring assembly, said second setof three cables being guided through pulleys mounted to said inner ringat substantially 120° with respect to each other and constrained to beparallel to each other between said end effector and said inner ring,wherein the winch retracts or deploys all three cables simultaneouslyand keeps the cable lengths between the inner ring and the end-effectorequal so that when said positioning mechanism moves said end effector toa selected position in its workspace, said second set of three cablesmaintains said end effector in a plane parallel to the plane of saidinner ring.

[0041] The present invention also provides a robotic mechanism,comprising:

[0042] an end effector, a post having opposed ends and an adjustablelength being pivotally connected at one of said opposed ends to the endeffector;

[0043] a support base, the other end of said opposed ends of the postbeing pivotally connected on a top surface of said support base;

[0044] a set of three cables each connected at one end thereof to theend of said post pivotally connected to said end effector and the otherends of each of said first set of three cables being attached topositioning means mounted on said support base for pulling said cablesto position said end effector in a selected position in space;

[0045] a first longitudinal shaft having a first longitudinal axis and apulley being rigidly mounted on each end of said first shaft, said firstlongitudinal shaft being mounted on a bottom surface of said supportbase and parallel to said support base, the first longitudinal shaft ispassing through a first sleeve, a first rotational spring mounted fromone end to the first sleeve and from the other end to the firstlongitudinal shaft for applying a constant torque to the fistlongitudinal shaft, including a first motor connected to said firstlongitudinal shaft for rotating said first longitudinal shaft about anaxis parallel to the said support base and normal to said firstlongitudinal shaft, a second longitudinal shaft having a secondlongitudinal axis and a pulley rigidly mounted on each end of saidsecond shaft, said second longitudinal shaft being mounted on the bottomsurface of said support base and parallel thereto and oriented so saidfirst longitudinal axis is perpendicular to said second longitudinalaxis, the second longitudinal shaft is passing through a second sleeve,a second rotational spring mounted from one end to the sleeve and fromthe other end to the second longitudinal shaft applies a constant torqueto the second longitudinal shaft, including a second motor connected tosaid second longitudinal shaft for rotating said second longitudinalshaft about an axis parallel to the said support base and normal to saidsecond longitudinal shaft; and

[0046] a first pair of cables with each cable connected at one endthereof to said end effector and the other end of one of the cablesbeing collected by one of the pulleys at the end of the firstlongitudinal shaft and the other end of the other cable being collectedby the other pulley at the other end of the first longitudinal shaft,the first rotational spring mounted in the first sleeve 148 whichapplies torque to the first longitudinal shaft has both the pulleysrotate and collect the first pair of cables so that the lengths of thecables of the said first pair of cables remain the same and therefore aparallelogram is maintained by the first pair of cables, a second pairof cables with each cable connected at one end thereof to said endeffector and the other end of one of the cables being collected by oneof the pulleys at the end of the second longitudinal shaft and the otherend of the other cable being collected or deployed by the other pulleyat the other end of the second longitudinal shaft as said secondlongitudinal shaft is rotated by the torque provided by the rotationalspring mounted in the second sleeve 146 and therefore the length of thecables of said second pair of cables remains the same and thus aparallelogram is maintained by the second pair of cables, and whereinsaid cables of said first pair of cables are parallel and said cables ofthe second pair of cables are parallel so that a plane defined by saidend effector is maintained parallel to a plane defined by said twolongitudinal shafts.

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The present invention will now be described by way of exampleonly, reference being had to the accompanying drawings in which:

[0048]FIG. 1 is a perspective view of a three degree of freedom (DOF)wire actuated parallel robot using active cables constructed inaccordance with the present invention;

[0049]FIG. 2 is a perspective view of a three degree of freedom wireactuated parallel robot using passive cables;

[0050]FIG. 3 is a perspective view of another embodiment of three degreeof freedom wire actuated parallel robot using passive cables;

[0051]FIG. 4 is a perspective view of a six DOF parallel mechanism usingpassive cables;

[0052]FIG. 5 is a perspective view of a three-to-five DOF parallelmechanism using active and passive cables;

[0053]FIG. 6 shows a top view (view A-A in FIG. 5) of the base platformand rings of the mechanism of FIG. 5;

[0054]FIG. 7(a) shows an overall perspective view of the configurationof active cables in the mechanism of FIG. 5;

[0055]FIG. 7(b) shows a detailed view of the portion of FIG. 7(a) in thesquare box;

[0056]FIG. 8(a) shows an overall perspective view of the configurationof the passive cables in the mechanism of FIG. 5;

[0057]FIG. 8(b) shows a detailed view of a portion of the passive cablemechanism of FIG. 8(a);

[0058]FIG. 8(c) shows a side view of the passive cable configuration ofFIG. 8(a);

[0059]FIG. 9 is a perspective view showing the connection of passivecables to the bottom end of the center post;

[0060]FIG. 10 shows the mechanism of FIG. 5 in two positions, verticaland tilted at an angle from the vertical showing the moving platformremains parallel to the base platform;

[0061]FIG. 11(a) is an overall perspective view of a three-to-five DOFrobotic mechanism;

[0062]FIG. 11(b) is a close up detailed perspective view of the wiretensioning mechanism of the robotic mechanism of FIG. 11(a);

[0063]FIG. 12 is a top perspective view of the mechanism of FIG. 11aabsent the end effector and central post showing the tensioningmechanism for the passive cables used to maintain the moving platformparallel to the base;

[0064]FIG. 13 shows the configuration of active cables for positioningthe central post of the mechanism of FIG. 11;

[0065]FIG. 14 is a perspective view of a hybrid parallel mechanism usingseven active cables that can produce between three and five degrees offreedom for the moving platform;

[0066]FIG. 15 is a perspective view of the central extensible rod andthree active cables for the mechanism of FIG. 14;

[0067]FIG. 16 is a bottom view of the mechanism of FIG. 14;

[0068]FIG. 17 is a perspective view of three degree of freedom parallelplanar manipulator using active cable;

[0069]FIG. 18 is a bottom view of the moving platform componentconnection for planar manipulator;

[0070]FIG. 19 is a perspective view of two degree of freedom parallelplanar manipulator using an active cable;

[0071]FIG. 20 is a perspective view of a parallel planar manipulatorusing a passive cable;

[0072]FIG. 21 is a bottom view of three degree of freedom parallelplanar manipulator using a passive cable;

[0073]FIG. 22 shows the parallelism of the moving platform enforced bytwo parallelograms;

[0074]FIG. 23 is a perspective view of a two degree of freedom parallelplanar manipulator driven by passive cables with the orientationconstrained by a winch mechanism; and

[0075]FIG. 24 shows a perspective view of a three degree of freedomparallel planar manipulator driven by passive cables with theorientation controlled by a cam and a winch mechanism.

DETAILED DESCRIPTION OF THE INVENTION

[0076] 1. Three-Degree-of-Freedom Parallel Mechanism Using Active Cables

[0077] A three-degree-of-freedom parallel robotic mechanism using activecables constructed in accordance with the present invention is showngenerally at 20 in FIG. 1 and includes a moving platform 22 that isattached to base platform 24 using an extensible or telescoping centralpost 26 and three sets of parallel cables 28 with one end of each ofcable attached to platform 22 and the other ends of each pair of cablesattached to an associated winch assembly 30. Each winch assembly 30includes a drum 32 mounted for rotation in a frame 36 which is attachedto the base 24 to keep the drum 32 in place and also to guide the cables28 to the drum via two holes 39 located in the top plate 38 of the frame36. The extensible post 26 is attached to the platform 22 (end-effector)and base 24 by universal joints 34 at both ends of the post to preventthe rotation of the moving platform 22. The extensible center post 26applies a compression force between the platforms 22 and 24 using alinear actuator such as a hydraulically, pneumatically, and electricallypowered cylinder. Alternatively, a linear motor (active element) orusing a preloaded spring, or air pressure (passive element) may beemployed in alternative embodiments of the mechanism to maintain tensionof cables 28. Post 26 may be any one of a hydraulically, pneumatically,and electrically powered cylinder.

[0078] The motion of the moving platform 22 is controlled by the threepairs of active cables 28. The two cables of each pair of cables 28 areparallel to each other to make a parallelogram as shown by the closedloop of a-b-c-d in FIG. 1. A motor controller 31 is connected to themotors 33 for driving the motors as well as being connected toposition/velocity sensors on each of the drums 32. A computer 35attached to the controller 31 is used to program/command the controllerfor positioning the cables on each of the winches. A tool 37 is mountedon top of end effector 22 and is controlled by controller 31 or byseparate controller 41. When the end effector 22 is to be positioned ina selected location in its workspace, signals are sent by controller 31based on its existing program or command signals sent by computer 35which in turn moves the drums 32 in each winch 30 to either roll up theparallel cables 28 or release them, depending on the particular winchand where in the robotic workspace space the end effector 22 is to belocated. The lengths of the three pairs of the cables 28 are adjustedindependently to provide three degrees of freedom to the end effectorplatform 22.

[0079] Due to the three cable-parallelogram structures the movingplatform 22 will always be parallel to the base platform 24 and canundergo three translational degrees of motion. This is obtained becausethe edge a-b in parallelogram a-b-c-d (similarly in the other twoparallelograms) is always parallel to edge c-d that is parallel to baseplatform 24. Since the three intersecting edges (a-b and the other twosimilar edges) are always parallel to base platform 24, the movingplatform 22 remains parallel to base platform 24 regardless of thelengths of the pairs of cables 28. The lengths of each pair of cables 28are controlled independently by their associated rotating drums 32. Thelengths of each pair of cables 28 determines the center location of themoving platform 22 while the parallelograms keep the platform 22parallel to the base 24. The length of the central post 26 changesaccording to the location of the moving platform 22 and the compressionforce that is applied to the platform 22 from the central post 26.

[0080] 2. Three-Degree-of-Freedom Parallel Mechanism Using PassiveCables

[0081] A three-degree-of-freedom parallel robotic mechanism usingpassive cables constructed in accordance with the present invention isshown generally at 40 in FIG. 2 and includes moving platform 22 that isattached to base platform 24 using an extensible or telescoping centralpost 26. As with robot 20 in FIG. 1, the extensible post 26 is attachedto the platforms 22 and 24 by universal joints 34 at both ends of thepost to prevent the rotation of the moving platform 22. There are threepairs of fixed-length cables 42 attached to the moving platform 22 andeach pair of cables 42 forms a parallelogram a-b-c-d as seen in FIG. 2.The ends of each pair of cables 42 at the lower edge c-d of theparallelogram are connected to a link arm 44 using a revolute joint 46having an axis of rotation coincident with c-d. Each link arm 44 isconnected to a bracket 48 using another revolute joint 50 whose axis ofrotation is parallel to axis c-d. Frame 48 is attached to base 24 andlink arm 44 is rotated by an actuator such as an electrical motor (notshown in the figure). When link arm 44 is rotated about the rotationalaxis of the lower revolute joint 50, the upper axis a-b remains parallelto axis c-d which guarantees the moving platform 22 stays parallel tothe base platform 24 during any motion.

[0082] The same reasoning as to why the moving platform 22 remainsparallel with the base 24 in apparatus 20 in FIG. 1 applies to base 24and platform 22 of apparatus 40 regardless of the angles of arms 44.Thus platform 22 has a pure translational motion along the X, Y andZ-axes. The extendable center post 26 pushes the platform 22 away fromthe base 24 and generates tension in the pairs of cables 42 whichprevents them from becoming slack.

[0083]FIG. 3 shows an alternative embodiment at 60 of a robotconstructed following the same principle as robot 40 with the differencebeing link arm 44 (FIG. 2) is replaced by actuators that move edge c-dand the other two similar axes of the parallelograms parallel to thebase platform. As an example, connection rod 46 can be movedhorizontally or vertically by a linear actuator attached thereto (notshown) to change the location of rod 46 without modifying its angle withthe base 24. Similarly, connection rod 46 can be attached to a rotaryactuator for movement in a plane parallel to the base platform 24 toprovide the desired movement of the platform 22. For all these differentmotions as long as the axis of connection rods 46 are maintainedparallel to the base platform 24 the mechanism 60 will have threetranslational degrees of freedom in the X, Y and Z directions.

[0084] Mechanisms 40 and 60 also include a computer controlled motorcontroller (not shown) such as computer 35 connected to controller 31shown in FIG. 1.

[0085] 3. Six-Degree-of-Freedom Parallel Mechanism Using Passive Cables

[0086] A generalization of the design shown in FIG. 3 can be extended toa 6 degree of freedom robot as shown generally at 66 in FIG. 4. In thisdesign the extendible center post 26 is attached to the base 24 andmoving platform 22 by two spherical joints 56, or one spherical jointand one universal joint instead of two universal joints as is used inmechanisms 20, 40, and 60 in FIGS. 1, 2, and 3. The parallelograms inthe previous mechanisms 20, 40 and 60 defined by the pairs of parallelcables are used to impose mechanical constraints to eliminate threerotational degrees of freedom. In the six degree of freedom robot 66 theends of cables 42 are connected to separate actuators to provide threeextra degrees of freedom. In this design the six cables 42 are stillpassive and are connected at one end to an associated arm 44 and at theother end to moving platform 22. Each link arm 44 is connected to aframe 48 with a revolute joint 50. Frame 48 is attached to the base 24and link arm 44 is rotated by an actuator such as an electrical motornot shown but similar to the motors and controller shown in FIG. 1. Whenlink arm 44 is rotated the end points of the cables connected to arms 44change and as a result the position and orientation of the movingplatform 22 can be controlled. The central extensible post 26 applies apushing force through a spring or air cylinder (not shown in the figure)to keep cables 42 in tension. It should be noted that the design is notlimited to the use of assembly 44, 48 and 50 to move the end points ofthe cables and any mechanism and actuator (linear or rotary) can be usedto achieve the same number of degrees of freedom, as discussed withrespect to the mechanism of FIG. 3. Also, there are no limitations onthe location of cable 42 attachment to the moving platform, however,these locations will change the overall workspace of the robot.Mechanism 66 also include a computer controlled motor controller (notshown) such as computer 35 connected to controller 31 shown in FIG. 1for controlling each of the actuators.

[0087] The six degree-of-freedom robotic mechanism of FIG. 4 may beconverted to a five degree-of-freedom device by replacing sphericaljoints 56 connecting post 26 to base 24 and end effector 22 withuniversal joints and removing one of the six cables 42 and associatedlink arm 44 and motor. The five degrees of freedom will include threetranslational and two rotational motions (pitch and yaw). Thereplacement of the spherical joints with universal joints will eliminatethe roll motion of moving platform 22 with respect to post 26 and fixedplatform 24.

[0088] 4. Three-to-Five DOF Parallel Mechanism Using Passive and ActiveCables

[0089] Referring to FIG. 5, there is shown generally at 70 a hybridparallel mechanism using a combination of active and passive cables toprovide five degrees of freedom for moving platform 22, including threetranslational and two rotational motions. In this embodiment of theinvention, base platform 24 includes two rings 76 and 74. The top viewof base 24 and the two rings is shown in FIG. 6. Ring 76 is attached tobase platform 24 by two revolute joints 87 diametrically located onopposite sides of ring 76 and having coextensive or coincident axis ofrotation. Revolute joints 87 are fixed in ring 76, and held by collarson base 24.

[0090] Actuator 84 is mounted on base 24 and its shaft is connected toone of the revolute joints 87 to provide a relative rotational motion ofring 76 with respect to base 24 so that ring 76 can be rotated out ofthe plane of base 24. Similarly, ring 74 is attached to ring 76 by tworevolute joints 86 diametrically located on opposite sides of ring 74and with revolute joints 86 having coextensive or coincident axis ofrotation. The revolute joints 86 are fixed in ring 76 and held bycollars in ring 74. The coextensive axes of rotation of the two revolutejoints 86 are normal to the coextensive axes of rotation of the tworevolute joints 87. Actuator 82 is mounted on ring 74 and its shaft isconnected to one of the revolute joints 86 to provide a relativerotational motion between rings 74 and 76 for rotating ring 74 out ofthe plane defined by ring 76. As a result, ring 74 is connected to base24 through ring 76 and has two rotational degrees of freedom (pitch andyaw) and its orientation is set by motors 82 and 84.

[0091] At the center of ring 74 there is collar 78 which is attached toring 74 by a universal joint 80. When the planes of rings 74, 76 are inthe same plane as base 24 and collar 78 is normal to the base the axesof rotation of universal joint 80 and revolute joints 86 and 87 are allin a single plane. Also, center post 72 can only slide in collar 78without any rotation. Platform 22 (FIG. 5) is connected to center post72 by universal joint 89 (FIG. 7(a)). Universal joint 89 prevents therotation of platform 22 with respect to the longitudinal axis of centerpost 72.

[0092] Referring again to FIG. 7(a), the top end of center post 72 isattached to three active cables 88 which are used to orient the centerpost 72 in space. FIG. 7(a) shows the mechanism without the passivecables 98 and movable platform 22 to show more clearly the active cables88. The active cables 88 are attached at one end thereof to the tip ofcenter post 72. Referring particularly to FIG. 7(b), each of the activecables 88 is pulled and accumulated using an associated winch assemblythat includes a pulley 92 and a motor 90 which rotates the pulley.Pulley 92 and motor 90 of each winch assembly is mounted in housing 96which is attached to the base platform 22 and each of the cables 88passes through a hole 94 located in the top of the associated housing96. The tip of center post 72 can be moved to any point in the workspaceby changing the length of active cables 88. The center post 72 applies apushing force to cables 88 to keep them in tension at all times. Thisforce can be generated by means of passive elements such as spring 73which applies the force between collar 78 and center post 72. In analternative embodiment an active element such as a linear motor (notshown in the figures) may be used instead.

[0093] There are three passive cables 98 (best seen in FIGS. 8(a) and8(b)) attached at one end to the moving platform 22 and at the other endto the bottom end of center post 72 (see FIG. 9). Passive cables 98 areparallel to each other in the section between ring 74 and platform 22(FIG. 10) and are used to maintain the moving platform 22 parallel toring 74 so that any orientation of ring 74 transfers to platform 22.

[0094] Referring to FIG. 8(a), the passive cables 98 from platform 22are guided through pulleys 100 which are mounted to brackets 103 (seeFIG. 8(b)), which in turn are attached to ring 74 using revolute joints(not shown). The revolute joints allow the pulleys 100 to adjustthemselves with respect to the direction of the associated cables 98.

[0095] Three other pulleys 104 (see FIG. 9) are mounted in brackets 106which are mounted on a frame 108 which is attached to collar 78. Theaxes of pulleys 100 are in the same plane which passes through thecenter of universal joint 80 (FIG. 6). Also, the axes of pulleys 104 arein the same plane which passes through universal joint 80. Theseconditions are required to keep the platform 22 parallel to ring 74.

[0096] Pulleys 104 guide the cables 98 to their attachment point at thebottom end of center post 110. Three springs 112 are in series withcables 98. These three springs 112 are used to provide tension inpassive cables 98 and also compensate for small changes in the length ofcables 98 when the center post 72 deviates from its vertical position.

[0097] The three passive cables 98 maintain the platform parallel toring 74 as shown in FIG. 10 for a 2D situation. In an idealconfiguration, pulleys 100 and 104 have zero diameters. As seen in thefigure, regardless of the angle of 72 BC=EF and DC=DE. Since the overalllength of the cables ABCD and GFED are equal, AB=GF all the time. Thisconstitutes a parallelogram which guarantees end effector 22 staysparallel to base platform 24.

[0098] The embodiment shown at 70 in FIG. 5 is a five degree-of-freedommechanism that has three translational motions of the moving platform 22that are provided by actuators 90 and active cables 88, and the tworotational degrees of freedom are provided by actuators 82 and 84 toorient moving platform 22. The translational and rotational motions ofthe moving platform are independent which result in simple kinematics ofthe mechanism. Mechanism 70 can be converted into a three degree offreedom mechanism by removing rings 74 and 76 and connecting pulleys 100and their frames directly to base 24. In this configuration platform 22is always parallel to the base and its location can be changed by activecables 88 and motors 90. Alternatively, a three degree of freedommechanism can be obtained by locking rings 74 and 76 with respect tobase 24.

[0099] 5. Alternative Three-to-Five DOF Parallel Mechanism Using ActiveCables

[0100] Referring to FIG. 11(a), there is shown generally at 200 a hybridparallel mechanism using a combination of active and passive cables toprovide five degrees of freedom for moving platform 22, including threetranslational degrees of freedom and two rotational degrees of freedom.The overall structure of mechanism 200 is very similar to mechanism 70in FIG. 5 except for the central post 26 and the way passive cables 98keep the moving platform 22 parallel to ring 74. The central post inthis design is extensible and connected to both moving platform 22 andring 74 with universal joints. It further applies an active or passivepushing force to the platform and ring via a spring or air cylinder (notshown in the figure) or it could be a linear motor to continuouslyadjust the force.

[0101] A close-up of the mechanism that keeps platform 22 parallel toring 74 is shown in FIGS. 11b and 12. Passive cables 98 are guided to awinch mechanism which includes a drum 97 mounted for rotation in a frame107 and driven by a motor 99. Frame 107 is attached to ring 74. Threepulleys 100 are mounted on frames 106 that are connected to ring 74 byrevolute joints 103 and spaced 1200 with respect to each other aroundring 74. Two pulleys 101 are mounted on associated frames 105 that areconnected directly to ring 74. These two pulleys 101 receive two of thecables 98 from two of the pulleys 100 which are then wrapped on drum 97.Cable 98 from the third pulley 100 goes directly to drum 97, best seemin FIG. 12. The cables 98 are wound on drum 97 by applying a torquegenerated by passive elements like rotational springs or active elementssuch as electrical or air motors shown schematically by 99. As seen inFIG. 12 the lengths of cables 98 between pulleys 100 and drum 97 areindependent from the position and orientation of platform 22. Also,cables 98 are wrapped around one single drum 97 and as a result thechange in the lengths of cables 98 between pulleys 100 and platform 22will be the same in any robot's configurations. Now, if cables 98 areattached to platform 22 such that their lengths between pulleys 100 andconnection points on platform 22 become equal and parallel to thecentral post 26, each two cables 98 will make a parallelogram andtherefore platform 22 will remain parallel to ring 74 regardless of itsposition in the workspace.

[0102]FIG. 13 shows the arrangement of the active cables 88 that are thesame as the arrangement of the active cables in mechanism 70 in FIG.7(a). Referring again to FIG. 11a, mechanism 200 is a five degree offreedom mechanism that includes three translational degrees of freedomof the moving platform 22 provided by actuators 90 and active cables 88,and the two rotational degrees of freedom provided by actuators 82 and84 to orient moving platform 22 in its workspace. The translational androtational motions of the moving platform 22 are independent of eachother which results in simple kinematics of the mechanism. Mechanism 200may be converted into a three degree of freedom mechanism by removingrings 74 and 76 and connecting pulleys 100 and their frames directly tobase 24. This way platform 22 is always parallel to the base 24 and itslocation can be changed by changing the length of active cables 88 usingmotors 90.

[0103] In summary, the embodiment shown in FIGS. 11, 12 and 13 is a 5dof mechanism. In this mechanism the second set of cables are notattached to the bottom end of the post. They are pulled and collected bywinch 97. There are five pulleys mounted on the inner ring in order toguide the three cables to the winch. This winch pulls and collects allthree cables simultanously and hence keeps the cable lengths between theinner ring and the end-effector equal. Therefore, the end-effector staysparallel to the inner ring plane. Winch 97 can be connected to a motoror to a rotational spring in order to pull cables and keep them intension. In this mechanism the post can be as simple as the mechanismsof FIGS. 1 to 5.

[0104] 6. Three-to-five DOF Parallel Mechanism Using Active Cables

[0105]FIG. 14 shows a hybrid parallel mechanism at 120 using sevenactive cables that can produce between 3 and 5 degrees of freedom forthe moving platform 22. In this embodiment, the moving platform 22, baseplatform 24, and extensible center post 26 and universal joint 34 aresimilar to the previous embodiments. Three active cables 122 as shown inFIGS. 14 and 15 are attached at one end to the top of extensible centerpost 26 and the other ends are attached to winches 124 which are mountedin bracket frames 126 attached to platform 24. Winches 124, whichcontrol the lengths of cables 122 control the end location of theextensible rod in the space.

[0106] Referring particularly to FIGS. 14 and 16, two pairs of cables130 and 132 form two parallelograms. The pair of cables 130 are pulledand collected by two pulleys 136 mounted on the ends of shaft 138. Thepair of cables 132 are pulled and collected by two pulleys 140 mountedon the ends of shaft 142. Both shafts 138 and 140 and the associatedpulleys mounted on the ends of the respective shafts form a single bodyand therefore, the two pulleys rotate simultaneously with the shaft.Shaft 142 rotates inside collar 146. There is also a source of constanttorque acting between shaft 142 and collar 146. This torque can beapplied by a spring which maintains the cables 132 in tension.Similarly, shaft 138 rotates inside a collar 148. There is also a sourceof constant torque acting between shaft 138 and collar 148 which may beapplied by a spring and this keeps the cables 130 in tension.Maintaining the shafts 138 and 142 parallel to base 24 and platform 22′ensures that the platform 22 is parallel to the base 24. Collars 146 and148 are mounted to frame 150 and collar 146 is connected to motor 152and collar 148 is connected to motor 154. The motors rotate the collarsconnected thereto and this rotation is directly transferred to theplatform 22 which alters the orientation of the platform 22.

[0107] Each of the two longitudinal shafts 138 and 142 mounted on thebottom surface of the support plane are responsible for forming aparallelogram. Each of these two shafts has two pulleys rigidlyconnected at the two ends. The two shafts are initially parallel to thesupport base plane and normal to each other. In FIG. 16, there are twosleeves shown as 146 and 148. The two shafts pass through these sleevesand can rotate about their longitudinal axis. There are also rotationalsprings (not shown in the figure) used to apply a torque between eachsleeve and its associated shaft. Therefore, the shafts are under apassive torque so that they pull and collect the cables. As a result,the two pairs of parallel cables remain in tension and build twoparallelograms which force the end-effector to be parallel with the twolongitudinal shafts. If we rotate sleeves 146, 148 about an axisparallel to the support base plane and normal to the longitudinal axesof the shafts using motors 152 and 154, the rotation will be directlytransferred to the end-effector because the end-effector has to stayparallel to the longitudinal axes of the shafts. Therefore, the twomotors control the orientation of the end-effector and the mechanismwill provide 5 degrees of freedom.

[0108] 7. Three DOF Planar Parallel Mechanism Using Active Cables

[0109] A general three degree of freedom planar parallel mechanism usingactive cables constructed in accordance with the presented invention isshown generally at 170 in FIG. 17. The moving platform, 22 is attachedto a base plate 172 by extensible or telescoping central post 174 andthree active cables 176, through a winch assembly. See FIG. 18 fordetails. The base plate 172 provides a reference for the moving platform22, and its function is identical to the base platform 24 of FIG. 1. Thecentral post 174 is connected by revolute joint 180 to the bottom ofmoving platform 22 having an axis of rotation 179 (see FIG. 18 fordetails), and base plate 172 by a revolute joint 178 with the pivotingaxes 179 of the revolute joints 178 and 180 being perpendicular to theworkspace of the robot. The out of plane moment induced on the movingplatform 22 is counter-balanced by these revolute joints. A clevis pintype of revolute joint is a reasonable choice for this component. Thecables 176 do not need to be coplanar but they must be held in tension.Cables 176 may be attached to platform 22 by revolute joints 183 havingaxis of rotation parallel to axis 179 of joint 180. The purpose of therevolute joints 183 is to reduce the amount of bending at the attachmentpoints on the cables 176 to platform 22 which can increase the life spanof the cables and joints. Other attachment devices such as eyelets maybe used as well to reduce the bending while using the same design. Thecentral post 174 is used to exert a tensile force on the cables 176.

[0110] Each of the three winch assemblies 188 used in apparatus 170comprises a drum 190 in a housing 192 with each drum being driven by amotor 194, with each housing 192 having a pilot hole 196 in its topsurface through which the associated cable 176 passes to be wound ondrum 190. This mechanism uses a pair of cables 176 (hence two winchassemblies 188) on one side of the central post 174 and at least onecable 176 and its associated winch 188 on the opposite side of post 174.As the motor 194 turns, the drum 190 takes up or releases its associatedcable 176. The pilot hole 196 is used to position and set a referencepoint for the cables. The positioning of the moving platform 22 iscontrolled directly by the amount of cable released by the drum. Acomputer controlled motor controller systems (not shown) such ascomputer 35 connected to controller 31 shown in FIG. 1 is used to adjustthe length of the active cables.

[0111] In mechanism 170 shown in FIG. 17, the two parallel cables aresimilar to the parallelograms in the other embodiments and as long astheir lengths remain the same the end effector 22 can only move parallelto the base. However, in this design we have considered two motors to beable to change both the orientation and location of the end effectorthrough three actuators.

[0112] 8. Two DOF Planar Parallel Mechanism Using Active Cables.

[0113] In mechanism 170 of FIG. 17, the cables 176 from the side of post174 having the two winches 188 side-by-side have the ability toconstraint the orientation of the moving platform 22. If these cablesare equal in length, the cables 176 and the moving platform 22 forms aparallelogram for the same reasoning as the apparatus shown in FIG. 1.Thus, the moving platform 22 will be parallel to the top plane 173 ofthe base plate 172. On the other hand, if cables 176 are different inlength, the combination of all three cables determines the orientationof the moving platform 22. Therefore, referring to FIG. 19, a twotranslational degree of freedom active cable mechanism shown generallyat 200 can be constructed by replacing the two adjacent winch assemblies188 shown on FIG. 17 with a two cable winch assembly 30 shown in FIG. 1.Note that the resulting mechanism requires only two motors 194 and 33only. In FIG. 19, a design with one drum and motor for the two cables onthe same side of post 174 maintains the orientation of end effector 22is fixed, which is parallel to the base 172 in FIG. 19. One of the twopaired cables could be longer or shorter with respect to the otherthereby inclining the end effector 22 and as long as the length ratio ofthe two cables remains fixed the orientation or angle of the endeffector 22 will remain constant.

[0114] 9. Three DOF Planar Parallel Mechanism Using Passive Cables

[0115] A general three degree of freedom planar parallel mechanism usingpassive cables in accordance with the present invention is showngenerally at 210 in FIG. 20. The moving platform 22 is attached to thebase plate 172 by extensible or telescoping central post 174 and threepassive cables 212 each connected at one end of the cables to threelink-arms 214 and the other ends connected to platform 22. Theconnections of the cables 212 and the central post 174 to movingplatform 22 is identical to the connections in mechanism 170 shown inFIGS. 17, 18 and 19. The connection of post 174 to base 172 is also thesame as in FIG. 17. Link-arms 214 are pivotally connected to base 172through revolute joints 218. Similar to the active cable counterpartmechanism 170 in FIG. 17, passive cable mechanism 210 also requires apair of the cables 212 on one side of the central post 174 and at leastone cable 212 on the opposite side. The side with two cables 212controls the orientation of the moving platform 22. If these cables wereequal in length and are parallel to each other, the cables and the tipsof the link-arms form two parallelograms. Therefore, the orientation ofmoving platform 22 will be fixed during movement of the end effector 22,and in the FIG. 20 it will be parallel to ground. On the other hand, ifthis pair of cables 212 is orientated differently, the combination ofall three cables determines the orientation of the moving platform 22.It should be pointed out that the motion of ends of the cables 212attached to arms 214 is not necessarily circular provided by arm 214,and it can be linear or any other complex trajectory generated bylinkage mechanisms. This is analogous to the motion of pins 46 in themechanism 60 illustrated in FIG. 3.

[0116] Referring to FIG. 21, a computer controlled motor controllersystem such as computer 35 connected to controller 31 shown in FIG. 1 isused to control the motor which drives the link arms 214. FIG. 21 showsa bottom view of the mechanism 210 with the motors 33 attached to thelower revolute joints 218 of the link-arms 214. The rigid link arms 214are offset to maximize the rotation of link arms 214 without anyinterference with each other. Increasing the rotation of link arms 214will minimize the size of the robot. This applies to the embodimentsshown in FIGS. 17 to 24. The orientation of the cables 212 is determinedby the amount of rotation on the link-arms 214. Coupled with the passivecables 212, the position and the orientation of the moving platform 22are controlled. The operating principal is similar to the mechanismillustrated in FIG. 2.

[0117] 9. Two DOF Planar Parallel Mechanism Using Passive Cables

[0118] The mechanism shown in FIG. 20 can be converted to a two degreeof freedom planar manipulator by synchronizing the motion of the pairedlink-arms. A timing belt (or equivalently a chain-sprocket drive) can beused for that purpose. The configuration can be made by attaching asheave to the revolute joint 218 and rigidly attach them to the link arm214. The synchronizing motion can be achieve by connecting the sheavewith a timing belt. A synchronized motion of the paired link-arms 214ensures the parallelism of the paired cables 212 that in turn restrictsorientation of the moving platform 22. As illustrated in FIG. 22, whentwo link-arms 214 are parallel, the close loops B-C-E-F and A-D-B-C formtwo parallelograms, which forces line A-D (attached to the movingplatform) to be parallel with line E-F (attached to the base plate).Hence, the rotating degree of freedom of the moving platform iseliminated, leaving two translational degrees of freedom to themechanism only.

[0119] 10. Hybrid Two DOF Planar Parallel Mechanism Using Passive Cablesfor Positioning and Active Cable for Orientation

[0120]FIG. 23 shows another alternative embodiment of a mechanism shownat 220 to achieve the parallelism of the moving platform 22. Inmechanism 220, the cables 212 that are attached to the moving platform22 are connected to a beam 222, which pivots about the free end of alink-arm 224. The orientation of the beam 222 is constrained using awinch assembly 226 that includes a pair of cables 228 attached to beam222, a drum 230, and a torsion spring (represented by a torsion load232). Since both cables 228 are connected to the same drum 230, theirlengths are always equal to each other. The torsion spring 232 isattached to the drum 230 to maintain tension in cables 228. Note thatdrum 230 is passive and its rotation depends on the orientation of arm224 orientation. Analogous to the configuration shown in FIG. 22, thedrum 230, the beam 222, the pairs of cables 228 and 212, and the movingplatform 22 form two parallelograms that ensure the parallelism betweenthe moving platform 22 and the base plate 172. Hence, the orientation ofthe moving platform 22 is maintained parallel to the ground.

[0121] 11. Hybrid Three DOF Planar Parallel Mechanism Using PassiveCables For Positioning And Active Cable For Orientation

[0122] Referring now to FIG. 24, another embodiment of the mechanismshown in FIG. 20 is shown at 240. Mechanism 240 is similar to mechanism220 of FIG. 23 but includes a cam 242 that routes one of the cables 228.The objective of cam 242 is to create a bias on the length of one of theactive cables 228 to provide a new degree of freedom to the robotmechanism of FIG. 23. Adjusting the bias in the cable will allow tocontrol the orientation of the moving platform 22. The operatingprincipal is similar to a cam-follower mechanism. The linear guide 119is used to induce a linear motion to cam 242 as shown in FIG. 24.

[0123] When the cam 242 moves towards the center of the mechanism, itroutes the inner active cable 228 around the cam face. This effectivelyshortened the length the routed active cable while leaving the otheractive cable untouched. The resulting effect is a distortion on theparallelogram formed by the active cables and the beam. The routed cablepulls the beam on one side and forces the beam to tilt towards therouted cable. As a result, the beam 222 will no longer be parallel toground, but is controlled by this cam 242. Since the moving platform isparallel to the beam, the orientation of the moving platform is alsocontrolled. The same operation can be performed on the other cable 228.When the cam 242 moves towards the edge of the robots, it pulls the beam222 on one side and forces the beam 222 to tilt towards the edge of therobot, which leads to the same rotation on the moving platform 22.

[0124] As used herein, the terms “comprises”, “comprising”, “including”and “includes” are to be construed as being inclusive and open ended,and not exclusive. Specifically, when used in this specificationincluding claims, the terms “comprises” and “comprising” and variationsthereof mean the specified features, steps or components are included.These terms are not to be interpreted to exclude the presence of otherfeatures, steps or components.

[0125] The foregoing description of the preferred embodiments of theinvention has been presented to illustrate the principles of theinvention and not to limit the invention to the particular embodimentillustrated. It is intended that the scope of the invention be definedby all of the embodiments encompassed within the following claims andtheir equivalents.

Therefore what is claimed is:
 1. A robotic mechanism, comprising: asupport base, an end effector and a biasing member having opposed endsand attached at one of said opposed ends to the support base andattached at the other of said opposed ends to the end effector; and atleast three cables each connected at a first end thereof to said endeffector and said at least three cables having second ends beingattached to an associated positioning mechanism for retracting ordeploying each of said at least three cables to position said endeffector in a selected position in space, said biasing member applyingforce on the end effector with respect to the support base formaintaining tension in said at least three cables.
 2. The roboticmechanism according to claim 1 wherein said at least three cables isthree pairs of cables, wherein said positioning mechanism includes threewinches with a winch associated with each pair of cables forindependently retracting or deploying each of said three pairs ofcables, each winch being attached to said support base, each winchincluding a pulley with said second ends of said three pairs of cablesbeing wrapped around a pulley in the associated winch, each winchincluding a motor connected to said pulley for rotating said pulley forwinding and unwinding the pair of cables attached thereto, each pair ofcables having the first ends of the two cables attached to theend-effector and the second ends of the two cables being attached to itsassociated winch in such a way that two cables of each pair of cablesare parallel to each other and define a parallelogram so that duringmovement of the end effector the orientation of the end effector remainsfixed so that the robotic mechanism has three degrees of freedom.
 3. Therobotic mechanism according to claim 1 including a computer controllerconnected to said positioning mechanism for synchronizing the movementof each motor with respect to the other motors to control movement ofsaid end-effector.
 4. The robotic mechanism according to claim 1 whereinsaid positioning mechanism includes three rigid link arms each havingfirst and second ends with the first end of each rigid link arm beingpivotally attached to said support base, and wherein said at least threecables is three pairs of cables with the first ends of each pair ofcables attached to the end-effector and the second ends of each pair ofcables being attached to the second ends of an associated rigid linkarm, and wherein said positioning mechanism includes actuator attachedto said first end of each rigid link arm for pivotally moving said firstend of each rigid support arm for moving said second end of each rigidlink arm for pulling said cables, each pair of cables having the firstends of the two cables attached to the end-effector and the second endsof the two cables being attached to its associated rigid link arm sothat the two cables of each pair of cables are parallel to each otherand define a parallelogram so that during movement of the end effectorthe orientation of the end effector remains fixed so that the roboticmechanism has three degrees of freedom.
 5. The robotic mechanismaccording to claim 4 wherein said first end of each rigid link arm ispivotally attached to said support base using a revolute joint.
 6. Therobotic mechanism according to claim 1 wherein said at least threecables is three pairs of cables with the first ends of each pair ofcables attached to the end-effector and the second ends of each pair ofcables being attached to an associated positioning mechanism includingan actuator for moving the second ends of the associated pair of cablesindependently of the other pairs of cables, each pair of cables havingthe first ends of the two cables attached to the end-effector and thesecond ends of the two cables being attached to its associated actuatorin such a way that two cables of each pair of cables are parallel toeach other and define a parallelogram so that the robotic mechanism hasthree degrees of freedom so that during movement of the end effector theorientation of the end effector remains fixed so that the roboticmechanism has three degrees of freedom.
 7. The robotic mechanismaccording to claim 4 including a computer controller connected to eachpositioning mechanism for synchronizing the movement of each actuatorwith respect to the other actuators to control movement of saidend-effector.
 8. The robotic mechanism according to claim 1 wherein saidbiasing member is a spring.
 9. The robotic mechanism according to claim1 wherein said biasing member is one of a hydraulically, pneumatically,and electrically powered cylinder having an adjustable length.
 10. Therobotic mechanism according to claim 1 wherein said biasing member ispivotally attached to said end-effector and said support base usinguniversal joints.
 11. A robotic mechanism, comprising: a support base,an end effector and a biasing member having opposed ends and pivotallyattached at one of said opposed ends to the support base and pivotallyattached at the other of said opposed ends to the end effector; and sixcables each connected at a first end thereof to said end effector andsaid six cables having second ends being attached to an associatedpositioning mechanism for moving the second ends of the associated cableindependently of the other cables, said biasing member applying force onthe end effector with respect to the support base for maintainingtension in said six cables, wherein movement of the second ends of thecables by the associated positioning mechanisms changes a position andorientation of the end effector so that the robotic mechanism has sixdegrees of freedom.
 12. The robotic mechanism according to claim 11wherein said positioning mechanism includes six rigid link arms eachhaving first and second ends with the first end of each rigid link armbeing pivotally attached to said support base and the second endattached to the second end of an associated cable, said positioningmechanism including an actuator engaged to said each rigid link arm forpivotally moving said rigid link arm for moving said cables to positionthe end-effector in a work-space.
 13. The robotic mechanism according toclaim 11 wherein said biasing member is pivotally attached to said endeffector and said support base with spherical joints.
 14. The roboticmechanism according to claim 11 wherein said biasing member is pivotallyattached to said end-effector and said support base with a sphericaljoint and a universal joint.
 15. The robotic mechanism according toclaim 12 wherein said first end of each rigid link arm is pivotallyattached to said support base using a revolute joint.
 16. The roboticmechanism according to claim 11 including a computer controllerconnected to each positioning mechanism for synchronizing the movementof each positioning mechanism with respect to the other positioningmechanisms to control movement of said end-effector.
 17. The roboticmechanism according to claim 11 wherein said biasing member is a spring.18. The robotic mechanism according to claim 11 wherein said biasingmember is one of a hydraulically, pneumatically, and electricallypowered cylinder having an adjustable length.
 19. Afive-degree-of-freedom robotic mechanism, comprising: a support base, anend-effector and a biasing member having opposed ends and pivotallyattached at one of said opposed ends to the support base with auniversal joint and pivotally attached at the other of said opposed endsto the end-effector with a universal joint; and five cables eachconnected at a first end thereof to said end effector and said fivecables having second ends being attached to an associated positioningmechanism for moving the second ends of the associated cableindependently of the other cables, said biasing member applying force onthe end effector with respect to the support base for maintainingtension in said five cables, wherein movement of the second ends of thecables by the associated positioning mechanisms changes a position andorientation of the end-effector.
 20. The robotic mechanism according toclaim 19 wherein said positioning mechanism includes five rigid linkarms each having first and second ends with the first end of each rigidlink arm being pivotally attached to said support base and the secondend attached to the second end of an associated cable, said positioningmechanism including an actuator engaged to said each rigid link arm forpivotally moving said rigid link arm for moving said cables to positionthe end-effector in a work-space.
 21. The robotic mechanism according toclaim 20 wherein said first end of each rigid link arm is pivotallyattached to said support base using a revolute joint.
 22. The roboticmechanism according to claim 19 including a computer controllerconnected to each positioning mechanism for synchronizing the movementof each positioning mechanism with respect to the other positioningmechanisms to control movement of said end-effector.
 23. The roboticmechanism according to claim 19 wherein said biasing member is a spring.24. The robotic mechanism according to claim 19 wherein said biasingmember is one of a hydraulically, pneumatically, and electricallypowered cylinder having an adjustable length.
 25. The robotic mechanismaccording to claim 1 wherein said at least three cables is three cables,and wherein said biasing member is pivotally attached to saidend-effector with a first revolute joint and is pivotally connected tosaid support base with a second revolute joint, the first and secondrevolute joints having axis of rotation with are parallel, and whereinsaid positioning mechanism includes three winches each associated withone of the cables for independently retracting or deploying itsassociated cable, each winch being attached to said support base, eachwinch including a pulley with said second end of its associated cablebeing wrapped around the pulley, each winch including a motor connectedto said pulley for rotating said pulley for retracting and deploying thecable attached thereto.
 26. The robotic mechanism according to claim 25wherein two of said winches are located adjacent to each other on oneside of the biasing member and the other winch is located on the otherside of the biasing member, and wherein the cable attached to a first ofthe two adjacent winches is attached to the end effector at a positionon the other side of the biasing member, and wherein the cable attachedto a second of the two winches is attached to the end effector at aposition on the same side of the biasing members as the second winch,and wherein the cable attached to the winch located on the other side ofthe biasing member is attached to the end effector at a positionadjacent to the first revolute joint and aligned with the axis ofrotation of the first revolute joint so that the robotic mechanism hasthree degrees of freedom.
 27. The robotic mechanism according to claim26 wherein said three cables are each attached to the end-effector usingthree revolute joints, and wherein each revolute joint has an axis ofrotation, the three revolute joints being attached to the end-effectorso the axis of rotation of each of the three revolute joints areparallel, and wherein the axis of rotation of the revolute jointattached to the end effector at the position adjacent to the firstrevolute joint has its axis of rotation collinear with the axis ofrotation of the first revolute joint.
 28. The robotic mechanismaccording to claim 25 wherein said biasing member is a spring.
 29. Therobotic mechanism according to claim 25 wherein said biasing member isone of a hydraulically, pneumatically, and electrically powered cylinderhaving an adjustable length.
 30. The robotic mechanism according toclaim 25 including a computer controller connected to each positionmechanism for controlling movement of said end-effector.
 31. The roboticmechanism according to claim 25 wherein two of said winches are locatedadjacent to each other on one side of the biasing member and the otherwinch is located on the other side of the biasing member, and whereinthe cable attached to a first of the two adjacent winches is attached tothe end effector at a position on the other side of the biasing member,and wherein the cable attached to a second of the two winches isattached to the end effector at a position on the same side of thebiasing members as the second winch, and wherein the cable attached tothe winch located on the other side of the biasing member is attached tothe end effector at a position adjacent to the first revolute joint andaligned with the axis of rotation of the first revolute joint, andwherein the two adjacent winches is a single common winch including acommon shaft upon which the two pulleys are mounted, and including acommon motor connected to said common shaft, and wherein the two cablesconnected to the two pulleys have a same length, and wherein the twocables connected to the two pulleys are parallel to each other so thatthe orientation of the end-effector is constrained to remain fixedduring movement of the end-effector so that the robotic mechanism hastwo degrees of freedom.
 32. The robotic mechanism according to claim 31wherein said three cables are each attached to the end-effector usingthree revolute joints, and wherein each revolute joint has an axis ofrotation, the three revolute joints being attached to the end-effectorso the axis of rotation of each of the three revolute joints areparallel, and wherein the axis of rotation of the revolute jointattached to the end effector at the position adjacent to the firstrevolute joint has its axis of rotation collinear with the axis ofrotation of the first revolute joint.
 33. The robotic mechanismaccording to claim 31 wherein said biasing member is a spring.
 34. Therobotic mechanism according to claim 31 wherein said biasing member isone of a hydraulically, pneumatically, and electrically powered cylinderhaving an adjustable length.
 35. The robotic mechanism according toclaim 31 including a computer controller connected to each positionmechanism for controlling movement of said end-effector.
 36. The roboticmechanism according to claim 1 wherein said at least three cables isthree cables, and wherein said biasing member is pivotally attached tosaid end-effector with a first revolute joint and is pivotally connectedto said support base with a second revolute joint, the first and secondrevolute joints having axis of rotation with are parallel, and whereinsaid positioning mechanism includes three rigid link arms each havingfirst and second ends with the first end of each support arm beingpivotally attached to said support base in such a way that the rigidlink arms pivot in planes parallel to each other, and wherein the firstends of each cable is attached to the end-effector and the second endsof each cable is attached to the second ends of an associated rigid linkarm, and wherein said positioning mechanism includes an actuatorattached to each rigid link arm for pivotally moving each rigid link armfor moving said cables thereby moving the end effector.
 37. The roboticmechanism according to claim 36 wherein two of said rigid link arms arelocated adjacent to each other on one side of the biasing member and theother winch is located on the other side of the biasing member, andwherein the cable attached to a first of the two adjacent rigid linkmembers is attached to the end effector at a position on the other sideof the biasing member, and wherein the cable attached to a second of thetwo adjacent rigid link members is attached to the end effector at aposition on the same side of the biasing members as the second rigidlink member, and wherein the cable attached to the rigid link memberlocated on the other side of the biasing member is attached to the endeffector at a position adjacent to the first revolute joint and alignedwith the axis of rotation of the first revolute joint.
 38. The roboticmechanism according to claim 37 wherein said three cables are eachattached to the end-effector using three revolute joints, and whereineach revolute joint has an axis of rotation, the three revolute jointsbeing attached to the end-effector so the axis of rotation of each ofthe three revolute joints are parallel, and wherein the axis of rotationof the revolute joint attached to the end effector at the positionadjacent to the first revolute joint has its axis of rotation collinearwith the axis of rotation of the first revolute joint.
 39. The roboticmechanism according to claim 36 wherein said first end of each rigidlink arm is pivotally attached to said support base using a revolutejoint.
 40. The robotic mechanism according to claim 37 wherein theactuator associated with each rigid link arm is connected to therevolute joint connected the rigid link arm to the support base, andincluding a computer controller connected to each actuator forcontrolling movement of said end-effector.
 41. The robotic mechanismaccording to claim 36 wherein each of the rigid link arms is movedindependently of the other rigid link arms so that the robotic mechanismhas three degrees of freedom.
 42. The robotic mechanism according toclaim 1 wherein said end-effector includes a mounting mechanism forreceiving a tool to be mounted on the end-effector.
 43. The roboticmechanism according to claim 36 including a synchronizing mechanismconnected to the two rigid link arms on the same side of the bias memberso that the two rigid link arms remain parallel to each other duringmovement so that the robotic mechanism has two degrees of freedom. 44.The robotic mechanism according to claim 1 wherein said at least threecables is three cables, and wherein said biasing member is pivotallyattached to said end-effector with a first revolute joint and ispivotally connected to said support base with a second revolute joint,the first and second revolute joints having axis of rotation with areparallel, and wherein said positioning mechanism includes first andsecond rigid link arms each having first and second ends with the firstend of the first and second rigid link arms being pivotally attached tosaid support base in such a way that the rigid link arms pivot in planesparallel to each other, including a winch having beam pivotally attachedto the second rigid link arm at a pivot connection point, and whereinthe first ends of each cable is attached to the end-effector and onecable is attached to the second end of the first rigid link arm andother two cables are attached to the beam with one cable attached on oneside of the pivot connection point and the other cable being attached tothe beam on the other side of the pivot connection, the winch includinga drum attached to the support base, and wherein the second ends of theother two cables are attached to said drum, the winch including a drumbiasing member for maintaining tension on the two cables attached to thedrum, and wherein said positioning mechanism includes an actuatorattached to each rigid link arm for pivoting each rigid link arm formoving the end effector, and wherein the two cables have the same lengthso that during movement of the end effector the orientation of the endeffector remains fixed so that the robotic mechanism has three degreesof freedom.
 45. The robotic mechanism according to claim 44 wherein thewinch includes a cam mounted on the support base with the cam beingengagable to one of the two cables in order to create a bias in thelength of said one of the two cables so that during movement of the endeffector the orientation of the beam, and therefore the end effector canbe varied thereby adding a new degree of freedom to the robot mechanism,and wherein the cam includes a cam actuator for moving the cam foradjusting the amount of bias in said one of the two cables.
 46. Therobotic mechanism according to claim 44 wherein said biasing member is aspring.
 47. The robotic mechanism according to claim 44 wherein saidbiasing member is one of a hydraulically, pneumatically, andelectrically powered cylinder having an adjustable length.
 48. A roboticmechanism, comprising: an end effector, a post having opposed ends beingpivotally connected at one of said opposed ends to the end effector; asupport base defining a plane and having a hole extending therethrough,an outer ring structure pivotally connected to said support base withinsaid hole for pivotal motion of said outer ring structure out of theplane of said support base, a first actuator for pivoting said outerring structure, an inner ring structure pivotally mounted to said outerring structure inside said outer ring structure, said inner ringstructure being concentric with said outer ring structure, a secondactuator for pivoting said inner ring structure, said inner ringstructure having an axis of rotation in the plane of the outer ring, andperpendicular to the axis of rotation of said outer ring structure, saidinner ring structure having a central web with a hole therethrough and auniversal joint mounted in said hole to the central web, the other endof said post being slidably mounted in said universal joint, bias meansconnected to said post for biasing said end effector away from saidsupport base; a first set of three cables each connected at one endthereof to said end effector and the other ends of said first set ofthree cables being attached to positioning means mounted on said supportbase for pulling said three cables independently of each other toposition said end effector in a selected position in space; and a secondset of three cables each connected at one end thereof to said endeffector and the other ends thereof being attached to the other end ofsaid post, said second set of three cables being mounted to said innerring at substantially 120° with respect to each other and constrained tobe parallel to each other between said end effector and said inner ringand wherein when said positioning means moves said end effector to aselected position in its workspace, said second set of three cablesmaintains said end effector in a plane parallel to the plane of saidinner ring.
 49. The robotic mechanism according to claim 48 including afirst set of three pulleys each pivotally mounted on said inner ringstructure at substantially 120° with respect to each other, andincluding a second set of three pulleys each pivotally mounted on saidcentral web at substantially 120° with respect to each other and inregistration with said first set of pulleys, wherein each pulley of saidfirst set of three pulleys guides one cable each of said second set ofthree cables to an associated pulley from said second set of threepulleys.
 50. The robotic mechanism according to claim 49 includingbiasing means associated with each cable of said second set of threecables for maintaining tension on each cable of said second set ofcables.
 51. A robotic mechanism, comprising: an end effector, a posthaving opposed ends being pivotally connected at one of said opposedends to the end effector using a universal joint, the post having anadjustable length; a support base defining a plane and having a holeextending therethrough, an outer ring structure pivotally connected tosaid support base within said hole for pivotal motion of said outer ringstructure out of the plane of said support base, a first actuator forpivoting said outer ring structure, an inner ring structure pivotallymounted to said outer ring structure inside said outer ring structure,said inner ring structure being concentric with said outer ringstructure, a second actuator for pivoting said inner ring structure,said inner ring structure having an axis of rotation in the plane of theouter ring, and perpendicular to the axis of rotation of said outer ringstructure, said inner ring structure having a central web with a holetherethrough and a universal joint mounted in said hole to the centralweb, the other end of said post being slidably mounted in said universaljoint,; a first set of three cables each connected at one end thereof tosaid end effector and the other ends of said first set of three cablesbeing attached to a positioning mechanism mounted on said support basefor pulling said three cables independently of each other to positionsaid end effector in a selected position in space; and a second set ofthree cables each connected at one end thereof to said end effector andthe other ends thereof being attached to, a winch mounted on saidcentral web of the inner ring assembly, said second set of three cablesbeing guided through pulleys mounted to said inner ring at substantially120° with respect to each other and constrained to be parallel to eachother between said end effector and said inner ring, wherein the winchretracts or deploys all three cables simultaneously and keeps the cablelengths between the inner ring and the end-effector equal so that whensaid positioning mechanism moves said end effector to a selectedposition in its workspace, said second set of three cables maintainssaid end effector in a plane parallel to the plane of said inner ring.52. A robotic mechanism, comprising: an end effector, a post havingopposed ends and an adjustable length being pivotally connected at oneof said opposed ends to the end effector; a support base, the other endof said opposed ends of the post being pivotally connected on a topsurface of said support base; a set of three cables each connected atone end thereof to the end of said post pivotally connected to said endeffector and the other ends of each of said first set of three cablesbeing attached to positioning means mounted on said support base forpulling said cables to position said end effector in a selected positionin space; a first longitudinal shaft having a first longitudinal axisand a pulley being rigidly mounted on each end of said first shaft, saidfirst longitudinal shaft being mounted on a bottom surface of saidsupport base and parallel to said support base, the first longitudinalshaft is passing through a first sleeve, a first rotational springmounted from one end to the first sleeve and from the other end to thefirst longitudinal shaft for applying a constant torque to the fistlongitudinal shaft, including a first motor connected to said firstlongitudinal shaft for rotating said first longitudinal shaft about anaxis parallel to the said support base and normal to said firstlongitudinal shaft, a second longitudinal shaft having a secondlongitudinal axis and a pulley rigidly mounted on each end of saidsecond shaft, said second longitudinal shaft being mounted on the bottomsurface of said support base and parallel thereto and oriented so saidfirst longitudinal axis is perpendicular to said second longitudinalaxis, the second longitudinal shaft is passing through a second sleeve,a second rotational spring mounted from one end to the sleeve and fromthe other end to the second longitudinal shaft applies a constant torqueto the second longitudinal shaft, including a second motor connected tosaid second longitudinal shaft for rotating said second longitudinalshaft about an axis parallel to the said support base and normal to saidsecond longitudinal shaft; and a first pair of cables with each cableconnected at one end thereof to said end effector and the other end ofone of the cables being collected by one of the pulleys at the end ofthe first longitudinal shaft and the other end of the other cable beingcollected by the other pulley at the other end of the first longitudinalshaft, the first rotational spring mounted in the first sleeve 148 whichapplies torque to the first longitudinal shaft has both the pulleysrotate and collect the first pair of cables so that the lengths of thecables of the said first pair of cables remain the same and therefore aparallelogram is maintained by the first pair of cables, a second pairof cables with each cable connected at one end thereof to said endeffector and the other end of one of the cables being collected by oneof the pulleys at the end of the second longitudinal shaft and the otherend of the other cable being collected or deployed by the other pulleyat the other end of the second longitudinal shaft as said secondlongitudinal shaft is rotated by the torque provided by the rotationalspring mounted in the second sleeve 146 and therefore the length of thecables of said second pair of cables remains the same and thus aparallelogram is maintained by the second pair of cables, and whereinsaid cables of said first pair of cables are parallel and said cables ofthe second pair of cables are parallel so that a plane defined by saidend effector is maintained parallel to a plane defined by said twolongitudinal shafts.
 53. The robotic mechanism according to claims 43wherein said end-effector includes a mounting mechanism for receiving atool to be mounted on the end-effector.